CORYPHODON. 



523 



the Coryphodontidce were obtained during my exploration in Northwestern 

 New Mexico, under the organization of the survey of Capt. Gr. M. Wheeler. 

 Portions of many others have since been obtained by Mr. Wortman 

 and myself in Wyoming. Those specimens which include astragali are 

 mostly referable to this genus, but a few from both regions belong to Bath- 

 modon. It has, however, generally happened that specimens which include 



Fig. 25. — Skull of Coryphodon eUpliunlopus, from below, jtli natural size. From Report Expl. Surv. West 



of 100th Mer., G. M. Wheeler, vol. iv. 



teeth do not possess astragali, and vice versa, so that I have been compelled 

 to disregard the generic position of the species for the time being, and have 

 relied chiefly on the mandibular teeth for the characters, owing to the more 

 irregular occurence of other elements; and the tubercles of the teeth are 

 not always constant. The following key expresses the relations of these 

 forms, most of which, perhaps all, are good species: 



I. The last inferior molar with three posterior cusps, the internal sometimes represented by 

 a ridge ; or the posterior inferior molars with an accessory cusp or tubercle on the inner side 

 between the crests (Coryphodon, Owen) : 



An internal tubercle ; last upper molar with an anterior cross crest and anterior external crest closely 



connected ; size largest C. anax. 



An internal conic cusp ; posterior crest oblique ; heel very small ; size medium C. cuspidatua. 



An internal crest ; posterior crest oblique; heel small; size medium C obliquiw. 



An internal tubercle ; posterior crest little oblique ; heel large; size large 0. lobatM. 



II. Posterior inferior molars without internal accessory tubercle. 

 a. Posterior inferior molars with small or no heel : 



Large ; posterior superior molar oval, with distinct straight posterior crest ; inferior molars elongate ; 



symphysis mandibuli produced and narrower ; premaxillary elongate C. latipes. 



Medium ; inferior molars nearly as wide as long ; premaxillary short C. Jatidena. 



aa. Posterior inferior molars with prominent or wide heel : 

 Medium ; posterior superior molar with posterior angle, and angulate posterior crest ; inferior molars 

 elongate; symphysis mandibuli broad and short; premaxillary elongate ; tusk trihedral 



C. elephantopiu. 



